Method and apparatus for mobility in wireless communication system

ABSTRACT

The present disclosure relates to method and apparatus for mobility in wireless communications. According to an embodiment of the present disclosure, a method performed by a wireless device in a wireless communication system comprises: performing a dual active protocol stack (DAPS) mobility procedure for a mobility from a source cell to a target cell while maintaining a radio link for the source cell; performing a radio link monitoring (RLM) comprising a monitoring of a number of consecutive out-of-sync indications received on a radio link for the source cell during the DAPS mobility procedure; and after detecting a radio link failure (RLF) for the source cell based on the RLM, stopping a transmission on the radio link for the source cell during the DAPS mobility procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119 (e), this application claims the benefit ofKorean Patent Applications No. 10-2019-0035029, filed on Mar. 27, 2019,No. 10-2019-0035048, filed on Mar. 27, 2019, and No. 10-2019-0035097,filed on Mar. 27, 2019, the contents of which are all herebyincorporated by reference herein in their entirety.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to method and apparatus for mobility inwireless communications.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

Work has started in international telecommunication union (ITU) and 3GPPto develop requirements and specifications for new radio (NR) systems.3GPP has to identify and develop the technology components needed forsuccessfully standardizing the new RAT timely satisfying both the urgentmarket needs, and the more long-term requirements set forth by the ITUradio communication sector (ITU-R) international mobiletelecommunications (IMT)-2020 process. Further, the NR should be able touse any spectrum band ranging at least up to 100 GHz that may be madeavailable for wireless communications even in a more distant future.

The NR targets a single technical framework addressing all usagescenarios, requirements and deployment scenarios including enhancedmobile broadband (eMBB), massive machine-type-communications (mMTC),ultra-reliable and low latency communications (URLLC), etc. The NR shallbe inherently forward compatible.

In a wireless communication system, there may be many cases in which aUE should perform a mobility from a source cell to a target cell. Anexample of the mobility may comprise a make-before break (MBB) mobilityin which both of a source cell link and a target cell link aremaintained during the mobility. During the MBB mobility, data can betransferred over the source cell link and the target cell link to andfrom the wireless device.

SUMMARY OF THE DISCLOSURE Technical Problem

An aspect of the present disclosure is to provide method and apparatusfor mobility in a wireless communication system.

Another aspect of the present disclosure is to provide method andapparatus for performing an MBB mobility in a wireless communicationsystem.

Another aspect of the present disclosure is to provide method andapparatus for performing an RLM during a MBB mobility procedure in awireless communication system.

Another aspect of the present disclosure is to provide method andapparatus for handling the RLM during the MBB mobility procedure in awireless communication system.

Another aspect of the present disclosure is to provide method andapparatus for handling RLF during the MBB mobility procedure in awireless communication system.

Technical Solution

According to an embodiment of the present disclosure, a method performedby a wireless device in a wireless communication system comprises:performing a dual active protocol stack (DAPS) mobility procedure for amobility from a source cell to a target cell while maintaining a radiolink for the source cell; performing a radio link monitoring (RLM)comprising a monitoring of a number of consecutive out-of-syncindications received on a radio link for the source cell during the DAPSmobility procedure; and after detecting a radio link failure (RLF) forthe source cell based on the RLM, stopping a transmission on the radiolink for the source cell during the DAPS mobility procedure.

According to an embodiment of the present disclosure, a wireless devicein a wireless communication system comprises: a transceiver; a memory;and at least one processor operatively coupled to the transceiver andthe memory, and configured to: perform a dual active protocol stack(DAPS) mobility procedure for a mobility from a source cell to a targetcell while maintaining a radio link for the source cell, perform a radiolink monitoring (RLM) comprising a monitoring of a number of consecutiveout-of-sync indications received on a radio link for the source cellduring the DAPS mobility procedure, and after detecting a radio linkfailure (RLF) on the radio link for the source cell based on the RLM,stop a transmission on the radio link for the source cell during theDAPS mobility procedure.

According to an embodiment of the present disclosure, a processor for awireless device in a wireless communication system is configured tocontrol the wireless device to perform operations comprising: performinga dual active protocol stack (DAPS) mobility procedure for a mobilityfrom a source cell to a target cell while maintaining a radio link forthe source cell; performing a radio link monitoring (RLM) comprising amonitoring of a number of consecutive out-of-sync indications receivedon a radio link for the source cell during the DAPS mobility procedure;and after detecting a radio link failure (RLF) on the radio link for thesource cell based on the RLM, stopping a transmission on the radio linkfor the source cell during the DAPS mobility procedure.

Advantageous Effect

The present disclosure can have various advantageous effects.

For example, a wireless device may perform an RLM on a source cellduring a DAPS mobility procedure and stop a transmission on the sourcecell after detecting an RLF on the source cell based on the RLM.Therefore, unnecessary transmission to the source cell and unnecessarymonitoring on a downlink from the source cell can be avoided, and thuspower consumption in the wireless device can be reduced.

For example, when a target cell receives a mobility complete messageincluding RLF indication of a source cell, the target cell can requestthe source cell to stop handling residual data on the source cell.Therefore, additional data interruption which can be occurred by thesource cell still trying to handle the residual data can be reduced.Additionally, after a mobility complete, the target cell may not need toconfigure RRC reconfiguration to release the source cell.

Advantageous effects which can be obtained through specific embodimentsof the present disclosure are not limited to the advantageous effectslisted above. For example, there may be a variety of technical effectsthat a person having ordinary skill in the related art can understandand/or derive from the present disclosure. Accordingly, the specificeffects of the present disclosure are not limited to those explicitlydescribed herein, but may include various effects that may be understoodor derived from the technical features of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows examples of 5G usage scenarios to which the technicalfeatures of the present disclosure can be applied.

FIG. 2 shows an example of a wireless communication system to which thetechnical features of the present disclosure can be applied.

FIG. 3 shows an example of a wireless communication system to which thetechnical features of the present disclosure can be applied.

FIG. 4 shows another example of a wireless communication system to whichthe technical features of the present disclosure can be applied.

FIG. 5 shows a block diagram of a user plane protocol stack to which thetechnical features of the present disclosure can be applied.

FIG. 6 shows a block diagram of a control plane protocol stack to whichthe technical features of the present disclosure can be applied.

FIG. 7 illustrates a frame structure in a 3GPP based wirelesscommunication system.

FIG. 8 illustrates a data flow example in the 3GPP NR system.

FIG. 9 shows an example of a dual connectivity (DC) architecture towhich technical features of the present disclosure can be applied.

FIG. 10 shows an example of a handover procedure to which technicalfeatures of the present disclosure can be applied.

FIG. 11 shows an example of a conditional handover procedure to whichtechnical features of the present disclosure can be applied.

FIG. 12 shows an example of a state of source protocol and targetprotocol for a DAPS handover before initiating a handover and a randomaccess to which technical features of the present disclosure can beapplied.

FIG. 13 shows an example of a state of source protocol and targetprotocol for a DAPS handover during a random access and a transmissionof a handover complete message to which technical features of thepresent disclosure can be applied.

FIG. 14 shows an example of a state of source protocol and targetprotocol for a DAPS handover after RAR and a release of the source RANnode to which technical features of the present disclosure can beapplied.

FIG. 15 shows an example of a method for an MBB mobility according to anembodiment of the present disclosure.

FIG. 16A and FIG. 16B show an example of a signal flow for RLM handlingduring a MBB handover according to an embodiment of the presentdisclosure.

FIG. 17 shows a UE to implement an embodiment of the present disclosure.The present disclosure described above for UE side may be applied tothis embodiment.

FIG. 18 shows another example of a wireless communication system towhich the technical features of the present disclosure can be applied.

FIG. 19 shows an example of an AI device to which the technical featuresof the present disclosure can be applied.

FIG. 20 shows an example of an AI system to which the technical featuresof the present disclosure can be applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technical features described below may be used by a communicationstandard by the 3rd generation partnership project (3GPP)standardization organization, a communication standard by the instituteof electrical and electronics engineers (IEEE), etc. For example, thecommunication standards by the 3GPP standardization organization includelong-term evolution (LTE) and/or evolution of LTE systems. The evolutionof LTE systems includes LTE-advanced (LTE-A), LTE-A Pro, and/or 5G newradio (NR). The communication standard by the IEEE standardizationorganization includes a wireless local area network (WLAN) system suchas IEEE 802.11a/b/g/n/ac/ax. The above system uses various multipleaccess technologies such as orthogonal frequency division multipleaccess (OFDMA) and/or single carrier frequency division multiple access(SC-FDMA) for downlink (DL) and/or uplink (UL). For example, only OFDMAmay be used for DL and only SC-FDMA may be used for UL. Alternatively,OFDMA and SC-FDMA may be used for DL and/or UL.

In the present disclosure, “A or B” may mean “only A”, “only B”, or“both A and B”. In other words, “A or B” in the present disclosure maybe interpreted as “A and/or B”. For example, “A, B or C” in the presentdisclosure may mean “only A”, “only B”, “only C”, or “any combination ofA, B and C”.

In the present disclosure, slash (/) or comma (,) may mean “and/or”. Forexample, “A/B” may mean “A and/or B”. Accordingly, “A/B” may mean “onlyA”, “only B”, or “both A and B”. For example, “A, B, C” may mean “A, Bor C”.

In the present disclosure, “at least one of A and B” may mean “only A”,“only B” or “both A and B”. In addition, the expression “at least one ofA or B” or “at least one of A and/or B” in the present disclosure may beinterpreted as same as “at least one of A and B”.

In addition, in the present disclosure, “at least one of A, B and C” maymean “only A”, “only B”, “only C”, or “any combination of A, B and C”.In addition, “at least one of A, B or C” or “at least one of A, B and/orC” may mean “at least one of A, B and C”.

Also, parentheses used in the present disclosure may mean “for example”.In detail, when it is shown as “control information (PDCCH)”, “PDCCH”may be proposed as an example of “control information”. In other words,“control information” in the present disclosure is not limited to“PDCCH”, and “PDDCH” may be proposed as an example of “controlinformation”. In addition, even when shown as “control information(i.e., PDCCH)”, “PDCCH” may be proposed as an example of “controlinformation”.

Technical features that are separately described in one drawing in thepresent disclosure may be implemented separately or simultaneously.

The terms used throughout the disclosure can be defined as thefollowings:

‘Mobility’ refers to a procedure for i) changing a PCell of a UE (i.e.,handover or PCell change), ii) changing a PSCell of a UE (i.e., SNchange or PSCell change), and/or iii) adding a PSCell for a UE (i.e., SNaddition or PSCell addition). Therefore, the mobility may comprise atleast one of a handover, an SN change or an SN addition. In other words,the mobility may comprise at least one of PCell change, PSCell change orPSCell addition. Throughout the disclosure, performing a mobility to atarget cell may refer to applying a mobility command of the target cellor applying RRC reconfiguration parameters in the mobility command ofthe target cell. Further, RRC reconfiguration and RRC connectionreconfiguration may be used interchangeably.

‘Conditional mobility’ refers to a mobility that is performed to atarget cell which satisfies a triggering condition among a plurality ofcandidate target cells. Throughout the disclosure, performing aconditional mobility to a target cell may refer to applying aconditional mobility command of a target cell which satisfies a mobilitycondition for the target cell among a plurality of candidate targetcells or applying RRC reconfiguration parameters in the conditionalmobility command of the target cell which satisfies a mobility conditionfor the target cell among the plurality of candidate target cells.

‘Mobility condition for a target cell’ refers to a triggering conditionfor a mobility to the target cell. That is, the mobility condition for atarget cell refers to a condition that should be satisfied fortriggering a mobility to the target cell. Mobility condition maycomprise at least one of an event, time-to-trigger (TTT), offset value,or threshold value(s). The mobility condition for an event may besatisfied if an entering condition for the event is satisfied for atleast the TTT. For example, the entering condition for event A3 may besatisfied if a signal quality for a target cell is better than that fora source cell more than or equal to the offset value. For anotherexample, the entering condition for event A4 may be satisfied if asignal quality for a target cell is better than a neighbor cellthreshold. For another example, the entering condition for event A5 maybe satisfied if a signal quality for a target cell is better than aneighbor cell threshold and a signal quality for a source cell is lowerthan a serving cell threshold.

Throughout the disclosure, the terms ‘radio access network (RAN) node’,‘base station’, ‘eNB’, ‘gNB’ and ‘cell’ may be used interchangeably.Further, a UE may be a kind of a wireless device, and throughout thedisclosure, the terms ‘UE’ and ‘wireless device’ may be usedinterchangeably.

The following drawings are created to explain specific embodiments ofthe present disclosure. The names of the specific devices or the namesof the specific signals/messages/fields shown in the drawings areprovided by way of example, and thus the technical features of thepresent disclosure are not limited to the specific names used in thefollowing drawings.

FIG. 1 shows examples of 5G usage scenarios to which the technicalfeatures of the present disclosure can be applied.

The 5G usage scenarios shown in FIG. 1 are only exemplary, and thetechnical features of the present disclosure can be applied to other 5Gusage scenarios which are not shown in FIG. 1.

Referring to FIG. 1, the three main requirements areas of 5G include (1)enhanced mobile broadband (eMBB) domain, (2) massive machine typecommunication (mMTC) area, and (3) ultra-reliable and low latencycommunications (URLLC) area. Some use cases may require multiple areasfor optimization and, other use cases may only focus on only one keyperformance indicator (KPI). 5G is to support these various use cases ina flexible and reliable way.

eMBB focuses on across-the-board enhancements to the data rate, latency,user density, capacity and coverage of mobile broadband access. The eMBBaims ˜10 Gbps of throughput. eMBB far surpasses basic mobile Internetaccess and covers rich interactive work and media and entertainmentapplications in cloud and/or augmented reality. Data is one of the keydrivers of 5G and may not be able to see dedicated voice services forthe first time in the 5G era. In 5G, the voice is expected to beprocessed as an application simply using the data connection provided bythe communication system. The main reason for the increased volume oftraffic is an increase in the size of the content and an increase in thenumber of applications requiring high data rates. Streaming services(audio and video), interactive video and mobile Internet connectivitywill become more common as more devices connect to the Internet. Many ofthese applications require always-on connectivity to push real-timeinformation and notifications to the user. Cloud storage andapplications are growing rapidly in mobile communication platforms,which can be applied to both work and entertainment. Cloud storage is aspecial use case that drives growth of uplink data rate. 5G is also usedfor remote tasks on the cloud and requires much lower end-to-end delayto maintain a good user experience when the tactile interface is used.In entertainment, for example, cloud games and video streaming areanother key factor that increases the demand for mobile broadbandcapabilities. Entertainment is essential in smartphones and tabletsanywhere, including high mobility environments such as trains, cars andairplanes. Another use case is augmented reality and informationretrieval for entertainment. Here, augmented reality requires very lowlatency and instantaneous data amount.

mMTC is designed to enable communication between devices that arelow-cost, massive in number and battery-driven, intended to supportapplications such as smart metering, logistics, and field and bodysensors. mMTC aims ˜10 years on battery and/or 1 million devices/km2.mMTC allows seamless integration of embedded sensors in all areas and isone of the most widely used 5G applications. Potentially by 2020,internet-of-things (IoT) devices are expected to reach 20.4 billion.Industrial IoT is one of the areas where 5G plays a key role in enablingsmart cities, asset tracking, smart utilities, agriculture and securityinfrastructures.

URLLC will make it possible for devices and machines to communicate withultra-reliability, very low latency and high availability, making itideal for vehicular communication, industrial control, factoryautomation, remote surgery, smart grids and public safety applications.URLLC aims ˜1 ms of latency. URLLC includes new services that willchange the industry through links with ultra-reliability/low latency,such as remote control of key infrastructure and self-driving vehicles.The level of reliability and latency is essential for smart gridcontrol, industrial automation, robotics, drones control andcoordination.

Next, a plurality of use cases included in the triangle of FIG. 1 willbe described in more detail.

5G can complement fiber-to-the-home (FTTH) and cable-based broadband (orDOCSIS) as a means of delivering streams rated from hundreds of megabitsper second to gigabits per second. This high speed can be required todeliver TVs with resolutions of 4K or more (6K, 8K and above) as well asvirtual reality (VR) and augmented reality (AR). VR and AR applicationsinclude mostly immersive sporting events. Certain applications mayrequire special network settings. For example, in the case of a VR game,a game company may need to integrate a core server with an edge networkserver of a network operator to minimize delay.

Automotive is expected to become an important new driver for 5G, withmany use cases for mobile communications to vehicles. For example,entertainment for passengers demands high capacity and high mobilebroadband at the same time. This is because future users will continueto expect high-quality connections regardless of their location andspeed. Another use case in the automotive sector is an augmented realitydashboard. The driver can identify an object in the dark on top of whatis being viewed through the front window through the augmented realitydashboard. The augmented reality dashboard displays information thatwill inform the driver about the object's distance and movement. In thefuture, the wireless module enables communication between vehicles,information exchange between the vehicle and the supportinginfrastructure, and information exchange between the vehicle and otherconnected devices (e.g. devices accompanied by a pedestrian). The safetysystem allows the driver to guide the alternative course of action sothat he can drive more safely, thereby reducing the risk of accidents.The next step will be a remotely controlled vehicle or self-drivingvehicle. This requires a very reliable and very fast communicationbetween different self-driving vehicles and between vehicles andinfrastructure. In the future, a self-driving vehicle will perform alldriving activities, and the driver will focus only on traffic that thevehicle itself cannot identify. The technical requirements ofself-driving vehicles require ultra-low latency and high-speedreliability to increase traffic safety to a level not achievable byhumans.

Smart cities and smart homes, which are referred to as smart societies,will be embedded in high density wireless sensor networks. Thedistributed network of intelligent sensors will identify conditions forcost and energy-efficient maintenance of a city or house. A similarsetting can be performed for each home. Temperature sensors, windows andheating controllers, burglar alarms and appliances are all wirelesslyconnected. Many of these sensors typically require low data rate, lowpower and low cost. However, for example, real-time high-definition (HD)video may be required for certain types of devices for monitoring.

The consumption and distribution of energy, including heat or gas, ishighly dispersed, requiring automated control of distributed sensornetworks. The smart grid interconnects these sensors using digitalinformation and communication technologies to collect and act oninformation. This information can include supplier and consumerbehavior, allowing the smart grid to improve the distribution of fuel,such as electricity, in terms of efficiency, reliability, economy,production sustainability, and automated methods. The smart grid can beviewed as another sensor network with low latency.

The health sector has many applications that can benefit from mobilecommunications. Communication systems can support telemedicine toprovide clinical care in remote locations. This can help to reducebarriers to distance and improve access to health services that are notcontinuously available in distant rural areas. It is also used to savelives in critical care and emergency situations. Mobile communicationbased wireless sensor networks can provide remote monitoring and sensorsfor parameters such as heart rate and blood pressure.

Wireless and mobile communications are becoming increasingly importantin industrial applications. Wiring costs are high for installation andmaintenance. Thus, the possibility of replacing a cable with a wirelesslink that can be reconfigured is an attractive opportunity in manyindustries. However, achieving this requires that wireless connectionsoperate with similar delay, reliability, and capacity as cables and thattheir management is simplified. Low latency and very low errorprobabilities are new requirements that need to be connected to 5G.

Logistics and freight tracking are important use cases of mobilecommunications that enable tracking of inventory and packages anywhereusing location based information systems. Use cases of logistics andfreight tracking typically require low data rates, but require a largerange and reliable location information.

NR supports multiple numerology (or, subcarrier spacing (SCS)) tosupport various 5G services. For example, when the SCS is 15 kHz, widearea in traditional cellular bands may be supported. When the SCS is 30kHz/60 kHz, dense-urban, lower latency and wider carrier bandwidth maybe supported. When the SCS is 60 kHz or higher, a bandwidth greater than24.25 GHz may be supported to overcome phase noise.

The NR frequency band may be defined as two types of frequency range,i.e., FR1 and FR2. The numerical value of the frequency range may bechanged. For example, the frequency ranges of the two types (FR1 andFR2) may be as shown in Table 1 below. For ease of explanation, in thefrequency ranges used in the NR system, FR1 may mean “sub 6 GHz range”,FR2 may mean “above 6 GHz range,” and may be referred to as millimeterwave (mmW).

TABLE 1 Frequency Range Corresponding Subcarrier designation frequencyrange Spacing FR1  450 MHz-6000 MHz  15, 30, 60 kHz FR2 24250 MHz-52600MHz 60, 120, 240 kHz

As mentioned above, the numerical value of the frequency range of the NRsystem may be changed. For example, FR1 may include a frequency band of410 MHz to 7125 MHz as shown in Table 2 below. That is, FR1 may includea frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more. Forexample, a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) ormore included in FR1 may include an unlicensed band. Unlicensed bandsmay be used for a variety of purposes, for example for communication forvehicles (e.g., autonomous driving).

TABLE 2 Frequency Range Corresponding Subcarrier designation frequencyrange Spacing FR1  410 MHz-7125 MHz  15, 30, 60 kHz FR2 24250 MHz-52600MHz 60, 120, 240 kHz

FIG. 2 shows an example of a wireless communication system to which thetechnical features of the present disclosure can be applied.

Referring to FIG. 2, the wireless communication system may include afirst device 210 and a second device 220.

The first device 210 includes a base station, a network node, atransmitting UE, a receiving UE, a wireless device, a wirelesscommunication device, a vehicle, a vehicle equipped with an autonomousdriving function, a connected car, a drone, an unmanned aerial vehicle(UAV), an artificial intelligence (AI) module, a robot, an AR device, aVR device, a mixed reality (MR) device, a hologram device, a publicsafety device, an MTC device, an IoT device, a medical device, afin-tech device (or, a financial device), a security device, aclimate/environmental device, a device related to 5G services, or adevice related to the fourth industrial revolution.

The second device 220 includes a base station, a network node, atransmitting UE, a receiving UE, a wireless device, a wirelesscommunication device, a vehicle, a vehicle equipped with an autonomousdriving function, a connected car, a drone, a UAV, an AI module, arobot, an AR device, a VR device, an MR device, a hologram device, apublic safety device, an MTC device, an IoT device, a medical device, afin-tech device (or, a financial device), a security device, aclimate/environmental device, a device related to 5G services, or adevice related to the fourth industrial revolution.

For example, the UE may include a mobile phone, a smart phone, a laptopcomputer, a digital broadcasting terminal, a personal digital assistant(PDA), a portable multimedia player (PMP), a navigation device, a slatepersonal computer (PC), a tablet PC, an ultrabook, a wearable device(e.g. a smartwatch, a smart glass, a head mounted display (HMD)). Forexample, the HMD may be a display device worn on the head. For example,the HMD may be used to implement AR, VR and/or MR.

For example, the drone may be a flying object that is flying by a radiocontrol signal without a person boarding it. For example, the VR devicemay include a device that implements an object or background in thevirtual world. For example, the AR device may include a device thatimplements connection of an object and/or a background of a virtualworld to an object and/or a background of the real world. For example,the MR device may include a device that implements fusion of an objectand/or a background of a virtual world to an object and/or a backgroundof the real world. For example, the hologram device may include a devicethat implements a 360-degree stereoscopic image by recording and playingstereoscopic information by utilizing a phenomenon of interference oflight generated by the two laser lights meeting with each other, calledholography. For example, the public safety device may include a videorelay device or a video device that can be worn by the user's body. Forexample, the MTC device and the IoT device may be a device that do notrequire direct human intervention or manipulation. For example, the MTCdevice and the IoT device may include a smart meter, a vending machine,a thermometer, a smart bulb, a door lock and/or various sensors. Forexample, the medical device may be a device used for the purpose ofdiagnosing, treating, alleviating, handling, or preventing a disease.For example, the medical device may be a device used for the purpose ofdiagnosing, treating, alleviating, or correcting an injury or disorder.For example, the medical device may be a device used for the purpose ofinspecting, replacing or modifying a structure or function. For example,the medical device may be a device used for the purpose of controllingpregnancy. For example, the medical device may include a treatmentdevice, a surgical device, an (in vitro) diagnostic device, a hearingaid and/or a procedural device, etc. For example, a security device maybe a device installed to prevent the risk that may occur and to maintainsafety. For example, the security device may include a camera, aclosed-circuit TV (CCTV), a recorder, or a black box. For example, thefin-tech device may be a device capable of providing financial servicessuch as mobile payment. For example, the fin-tech device may include apayment device or a point of sales (POS). For example, theclimate/environmental device may include a device for monitoring orpredicting the climate/environment.

The first device 210 may include at least one or more processors, suchas a processor 211, at least one memory, such as a memory 212, and atleast one transceiver, such as a transceiver 213. The processor 211 mayperform the functions, procedures, and/or methods of the first devicedescribed throughout the disclosure. The processor 211 may perform oneor more protocols. For example, the processor 211 may perform one ormore layers of the air interface protocol. The memory 212 is connectedto the processor 211 and may store various types of information and/orinstructions. The transceiver 213 is connected to the processor 211 andmay be controlled by the processor 211 to transmit and receive wirelesssignals.

The second device 220 may include at least one or more processors, suchas a processor 221, at least one memory, such as a memory 222, and atleast one transceiver, such as a transceiver 223. The processor 221 mayperform the functions, procedures, and/or methods of the second device220 described throughout the disclosure. The processor 221 may performone or more protocols. For example, the processor 221 may perform one ormore layers of the air interface protocol. The memory 222 is connectedto the processor 221 and may store various types of information and/orinstructions. The transceiver 223 is connected to the processor 221 andmay be controlled by the processor 221 to transmit and receive wirelesssignals.

The memory 212, 222 may be connected internally or externally to theprocessor 211, 212, or may be connected to other processors via avariety of technologies such as wired or wireless connections.

The first device 210 and/or the second device 220 may have more than oneantenna. For example, antenna 214 and/or antenna 224 may be configuredto transmit and receive wireless signals.

FIG. 3 shows an example of a wireless communication system to which thetechnical features of the present disclosure can be applied.

Specifically, FIG. 3 shows a system architecture based on anevolved-UMTS terrestrial radio access network (E-UTRAN). Theaforementioned LTE is a part of an evolved-UTMS (e-UMTS) using theE-UTRAN.

Referring to FIG. 3, the wireless communication system includes one ormore user equipment (UE) 310, an E-UTRAN and an evolved packet core(EPC). The UE 310 refers to a communication equipment carried by a user.The UE 310 may be fixed or mobile. The UE 310 may be referred to asanother terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN consists of one or more evolved NodeB (eNB) 320. The eNB 320provides the E-UTRA user plane and control plane protocol terminationstowards the UE 10. The eNB 320 is generally a fixed station thatcommunicates with the UE 310. The eNB 320 hosts the functions, such asinter-cell radio resource management (RRM), radio bearer (RB) control,connection mobility control, radio admission control, measurementconfiguration/provision, dynamic resource allocation (scheduler), etc.The eNB 320 may be referred to as another terminology, such as a basestation (BS), a base transceiver system (BTS), an access point (AP),etc.

A downlink (DL) denotes communication from the eNB 320 to the UE 310. Anuplink (UL) denotes communication from the UE 310 to the eNB 320. Asidelink (SL) denotes communication between the UEs 310. In the DL, atransmitter may be a part of the eNB 320, and a receiver may be a partof the UE 310. In the UL, the transmitter may be a part of the UE 310,and the receiver may be a part of the eNB 320. In the SL, thetransmitter and receiver may be a part of the UE 310.

The EPC includes a mobility management entity (MME), a serving gateway(S-GW) and a packet data network (PDN) gateway (P-GW). The MME hosts thefunctions, such as non-access stratum (NAS) security, idle statemobility handling, evolved packet system (EPS) bearer control, etc. TheS-GW hosts the functions, such as mobility anchoring, etc. The S-GW is agateway having an E-UTRAN as an endpoint. For convenience, MME/S-GW 330will be referred to herein simply as a “gateway,” but it is understoodthat this entity includes both the MME and S-GW. The P-GW hosts thefunctions, such as UE Internet protocol (IP) address allocation, packetfiltering, etc. The P-GW is a gateway having a PDN as an endpoint. TheP-GW is connected to an external network.

The UE 310 is connected to the eNB 320 by means of the Uu interface. TheUEs 310 are interconnected with each other by means of the PC5interface. The eNBs 320 are interconnected with each other by means ofthe X2 interface. The eNBs 320 are also connected by means of the S1interface to the EPC, more specifically to the MME by means of theS1-MME interface and to the S-GW by means of the S1-U interface. The S1interface supports a many-to-many relation between MMEs/S-GWs and eNBs.

FIG. 4 shows another example of a wireless communication system to whichthe technical features of the present disclosure can be applied.

Specifically, FIG. 4 shows a system architecture based on a 5G NR. Theentity used in the 5G NR (hereinafter, simply referred to as “NR”) mayabsorb some or all of the functions of the entities introduced in FIG. 3(e.g. eNB, MME, S-GW). The entity used in the NR may be identified bythe name “NG” for distinction from the LTE/LTE-A.

Referring to FIG. 4, the wireless communication system includes one ormore UE 410, a next-generation RAN (NG-RAN) and a 5th generation corenetwork (5GC). The NG-RAN consists of at least one NG-RAN node. TheNG-RAN node is an entity corresponding to the eNB 320 shown in FIG. 3.The NG-RAN node consists of at least one gNB 421 and/or at least oneng-eNB 422. The gNB 421 provides NR user plane and control planeprotocol terminations towards the UE 410. The ng-eNB 422 provides E-UTRAuser plane and control plane protocol terminations towards the UE 410.

The 5GC includes an access and mobility management function (AMF), auser plane function (UPF) and a session management function (SMF). TheAMF hosts the functions, such as NAS security, idle state mobilityhandling, etc. The AMF is an entity including the functions of theconventional MME. The UPF hosts the functions, such as mobilityanchoring, protocol data unit (PDU) handling. The UPF an entityincluding the functions of the conventional S-GW. The SMF hosts thefunctions, such as UE IP address allocation, PDU session control.

The gNBs 421 and ng-eNBs 422 are interconnected with each other by meansof the Xn interface. The gNBs 421 and ng-eNBs 422 are also connected bymeans of the NG interfaces to the 5GC, more specifically to the AMF bymeans of the NG-C interface and to the UPF by means of the NG-Uinterface.

A protocol structure between network entities described above isdescribed. On the system of FIG. 3 and/or FIG. 4, layers of a radiointerface protocol between the UE and the network (e.g. NG-RAN and/orE-UTRAN) may be classified into a first layer (L1), a second layer (L2),and a third layer (L3) based on the lower three layers of the opensystem interconnection (OSI) model that is well-known in thecommunication system.

FIG. 5 shows a block diagram of a user plane protocol stack to which thetechnical features of the present disclosure can be applied. FIG. 6shows a block diagram of a control plane protocol stack to which thetechnical features of the present disclosure can be applied.

The user/control plane protocol stacks shown in FIG. 5 and FIG. 6 areused in NR. However, user/control plane protocol stacks shown in FIG. 5and FIG. 6 may be used in LTE/LTE-A without loss of generality, byreplacing gNB/AMF with eNB/MME.

Referring to FIG. 5 and FIG. 6, a physical (PHY) layer belonging to L1.The PHY layer offers information transfer services to media accesscontrol (MAC) sublayer and higher layers. The PHY layer offers to theMAC sublayer transport channels. Data between the MAC sublayer and thePHY layer is transferred via the transport channels. Between differentPHY layers, i.e., between a PHY layer of a transmission side and a PHYlayer of a reception side, data is transferred via the physicalchannels.

The MAC sublayer belongs to L2. The main services and functions of theMAC sublayer include mapping between logical channels and transportchannels, multiplexing/de-multiplexing of MAC service data units (SDUs)belonging to one or different logical channels into/from transportblocks (TB) delivered to/from the physical layer on transport channels,scheduling information reporting, error correction through hybridautomatic repeat request (HARQ), priority handling between UEs by meansof dynamic scheduling, priority handling between logical channels of oneUE by means of logical channel prioritization (LCP), etc. The MACsublayer offers to the radio link control (RLC) sublayer logicalchannels.

The RLC sublayer belong to L2. The RLC sublayer supports threetransmission modes, i.e. transparent mode (TM), unacknowledged mode(UM), and acknowledged mode (AM), in order to guarantee various qualityof services (QoS) required by radio bearers. The main services andfunctions of the RLC sublayer depend on the transmission mode. Forexample, the RLC sublayer provides transfer of upper layer PDUs for allthree modes, but provides error correction through ARQ for AM only. InLTE/LTE-A, the RLC sublayer provides concatenation, segmentation andreassembly of RLC SDUs (only for UM and AM data transfer) andre-segmentation of RLC data PDUs (only for AM data transfer). In NR, theRLC sublayer provides segmentation (only for AM and UM) andre-segmentation (only for AM) of RLC SDUs and reassembly of SDU (onlyfor AM and UM). That is, the NR does not support concatenation of RLCSDUs. The RLC sublayer offers to the packet data convergence protocol(PDCP) sublayer RLC channels.

The PDCP sublayer belong to L2. The main services and functions of thePDCP sublayer for the user plane include header compression anddecompression, transfer of user data, duplicate detection, PDCP PDUrouting, retransmission of PDCP SDUs, ciphering and deciphering, etc.The main services and functions of the PDCP sublayer for the controlplane include ciphering and integrity protection, transfer of controlplane data, etc.

The service data adaptation protocol (SDAP) sublayer belong to L2. TheSDAP sublayer is only defined in the user plane. The SDAP sublayer isonly defined for NR. The main services and functions of SDAP include,mapping between a QoS flow and a data radio bearer (DRB), and markingQoS flow ID (QFI) in both DL and UL packets. The SDAP sublayer offers to5GC QoS flows.

A radio resource control (RRC) layer belongs to L3. The RRC layer isonly defined in the control plane. The RRC layer controls radioresources between the UE and the network. To this end, the RRC layerexchanges RRC messages between the UE and the BS. The main services andfunctions of the RRC layer include broadcast of system informationrelated to AS and NAS, paging, establishment, maintenance and release ofan RRC connection between the UE and the network, security functionsincluding key management, establishment, configuration, maintenance andrelease of radio bearers, mobility functions, QoS management functions,UE measurement reporting and control of the reporting, NAS messagetransfer to/from NAS from/to UE.

In other words, the RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers. A radio bearer refers toa logical path provided by L1 (PHY layer) and L2 (MAC/RLC/PDCP/SDAPsublayer) for data transmission between a UE and a network. Setting theradio bearer means defining the characteristics of the radio protocollayer and the channel for providing a specific service, and setting eachspecific parameter and operation method. Radio bearer may be dividedinto signaling RB (SRB) and data RB (DRB). The SRB is used as a path fortransmitting RRC messages in the control plane, and the DRB is used as apath for transmitting user data in the user plane.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. In LTE/LTE-A, when the RRCconnection is established between the RRC layer of the UE and the RRClayer of the E-UTRAN, the UE is in the RRC connected state(RRC_CONNECTED). Otherwise, the UE is in the RRC idle state (RRC_IDLE).In NR, the RRC inactive state (RRC_INACTIVE) is additionally introduced.RRC_INACTIVE may be used for various purposes. For example, the massivemachine type communications (MMTC) UEs can be efficiently managed inRRC_INACTIVE. When a specific condition is satisfied, transition is madefrom one of the above three states to the other.

A predetermined operation may be performed according to the RRC state.In RRC_IDLE, public land mobile network (PLMN) selection, broadcast ofsystem information (SI), cell re-selection mobility, core network (CN)paging and discontinuous reception (DRX) configured by NAS may beperformed. The UE shall have been allocated an identifier (ID) whichuniquely identifies the UE in a tracking area. No RRC context stored inthe BS.

In RRC_CONNECTED, the UE has an RRC connection with the network (i.e.E-UTRAN/NG-RAN). Network-CN connection (both C/U-planes) is alsoestablished for UE. The UE AS context is stored in the network and theUE. The RAN knows the cell which the UE belongs to. The network cantransmit and/or receive data to/from UE. Network controlled mobilityincluding measurement is also performed.

Most of operations performed in RRC_IDLE may be performed inRRC_INACTIVE. But, instead of CN paging in RRC_IDLE, RAN paging isperformed in RRC_INACTIVE. In other words, in RRC_IDLE, paging formobile terminated (MT) data is initiated by core network and paging areais managed by core network. In RRC_INACTIVE, paging is initiated byNG-RAN, and RAN-based notification area (RNA) is managed by NG-RAN.Further, instead of DRX for CN paging configured by NAS in RRC_IDLE, DRXfor RAN paging is configured by NG-RAN in RRC_INACTIVE. Meanwhile, inRRC_INACTIVE, 5GC-NG-RAN connection (both C/U-planes) is established forUE, and the UE AS context is stored in NG-RAN and the UE. NG-RAN knowsthe RNA which the UE belongs to.

NAS layer is located at the top of the RRC layer. The NAS controlprotocol performs the functions, such as authentication, mobilitymanagement, security control.

The physical channels may be modulated according to OFDM processing andutilizes time and frequency as radio resources. The physical channelsconsist of a plurality of orthogonal frequency division multiplexing(OFDM) symbols in time domain and a plurality of subcarriers infrequency domain. One subframe consists of a plurality of OFDM symbolsin the time domain. A resource block is a resource allocation unit, andconsists of a plurality of OFDM symbols and a plurality of subcarriers.In addition, each subframe may use specific subcarriers of specific OFDMsymbols (e.g. first OFDM symbol) of the corresponding subframe for aphysical downlink control channel (PDCCH), i.e. L1/L2 control channel. Atransmission time interval (TTI) is a basic unit of time used by ascheduler for resource allocation. The TTI may be defined in units ofone or a plurality of slots, or may be defined in units of mini-slots.

The transport channels are classified according to how and with whatcharacteristics data are transferred over the radio interface. DLtransport channels include a broadcast channel (BCH) used fortransmitting system information, a downlink shared channel (DL-SCH) usedfor transmitting user traffic or control signals, and a paging channel(PCH) used for paging a UE. UL transport channels include an uplinkshared channel (UL-SCH) for transmitting user traffic or control signalsand a random access channel (RACH) normally used for initial access to acell.

Different kinds of data transfer services are offered by MAC sublayer.Each logical channel type is defined by what type of information istransferred. Logical channels are classified into two groups: controlchannels and traffic channels.

Control channels are used for the transfer of control plane informationonly. The control channels include a broadcast control channel (BCCH), apaging control channel (PCCH), a common control channel (CCCH) and adedicated control channel (DCCH). The BCCH is a DL channel forbroadcasting system control information. The PCCH is DL channel thattransfers paging information, system information change notifications.The CCCH is a channel for transmitting control information between UEsand network. This channel is used for UEs having no RRC connection withthe network. The DCCH is a point-to-point bi-directional channel thattransmits dedicated control information between a UE and the network.This channel is used by UEs having an RRC connection.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels include a dedicated traffic channel (DTCH).The DTCH is a point-to-point channel, dedicated to one UE, for thetransfer of user information. The DTCH can exist in both UL and DL.

Regarding mapping between the logical channels and transport channels,in DL, BCCH can be mapped to BCH, BCCH can be mapped to DL-SCH, PCCH canbe mapped to PCH, CCCH can be mapped to DL-SCH, DCCH can be mapped toDL-SCH, and DTCH can be mapped to DL-SCH. In UL, CCCH can be mapped toUL-SCH, DCCH can be mapped to UL-SCH, and DTCH can be mapped to UL-SCH.

FIG. 7 illustrates a frame structure in a 3GPP based wirelesscommunication system.

The frame structure illustrated in FIG. 7 is purely exemplary and thenumber of subframes, the number of slots, and/or the number of symbolsin a frame may be variously changed. In the 3GPP based wirelesscommunication system, an OFDM numerology (e.g., subcarrier spacing(SCS), transmission time interval (TTI) duration) may be differentlyconfigured between a plurality of cells aggregated for one UE. Forexample, if a UE is configured with different SCSs for cells aggregatedfor the cell, an (absolute time) duration of a time resource (e.g. asubframe, a slot, or a TTI) including the same number of symbols may bedifferent among the aggregated cells. Herein, symbols may include OFDMsymbols (or CP-OFDM symbols), SC-FDMA symbols (or discrete Fouriertransform-spread-OFDM (DFT-s-OFDM) symbols).

Referring to FIG. 7, downlink and uplink transmissions are organizedinto frames. Each frame has Tf=10 ms duration. Each frame is dividedinto two half-frames, where each of the half-frames has 5 ms duration.Each half-frame consists of 5 subframes, where the duration Tsf persubframe is 1 ms. Each subframe is divided into slots and the number ofslots in a subframe depends on a subcarrier spacing. Each slot includes14 or 12 OFDM symbols based on a cyclic prefix (CP). In a normal CP,each slot includes 14 OFDM symbols and, in an extended CP, each slotincludes 12 OFDM symbols. The numerology is based on exponentiallyscalable subcarrier spacing Δf=2u*15 kHz. The following table shows thenumber of OFDM symbols per slot, the number of slots per frame, and thenumber of slots per for the normal CP, according to the subcarrierspacing Δf=2u*15 kHz.

TABLE 3 u Nslotsymb Nframe, uslot Nsubframe, uslot 0 14 10 1 1 14 20 2 214 40 4 3 14 80 8 4 14 160 16

The following table shows the number of OFDM symbols per slot, thenumber of slots per frame, and the number of slots per for the extendedCP, according to the subcarrier spacing Δf=2u*15 kHz.

TABLE 4 u Nslotsymb Nframe, uslot Nsubframe, uslot 2 12 40 4

A slot includes plural symbols (e.g., 14 or 12 symbols) in the timedomain. For each numerology (e.g. subcarrier spacing) and carrier, aresource grid of Nsize,ugrid,x*NRBsc subcarriers and Nsubframe,usymbOFDM symbols is defined, starting at common resource block (CRB)Nstart,ugrid indicated by higher-layer signaling (e.g. radio resourcecontrol (RRC) signaling), where Nsize,ugrid,x is the number of resourceblocks (RBs) in the resource grid and the subscript x is DL for downlinkand UL for uplink. NRBsc is the number of subcarriers per RB. In the3GPP based wireless communication system, NRBsc is 12 generally. Thereis one resource grid for a given antenna port p, subcarrier spacingconfiguration u, and transmission direction (DL or UL). The carrierbandwidth Nsize,ugrid for subcarrier spacing configuration u is given bythe higher-layer parameter (e.g. RRC parameter). Each element in theresource grid for the antenna port p and the subcarrier spacingconfiguration u is referred to as a resource element (RE) and onecomplex symbol may be mapped to each RE. Each RE in the resource grid isuniquely identified by an index k in the frequency domain and an index 1representing a symbol location relative to a reference point in the timedomain. In the 3GPP based wireless communication system, an RB isdefined by 12 consecutive subcarriers in the frequency domain.

In the 3GPP NR system, RBs are classified into CRBs and physicalresource blocks (PRBs). CRBs are numbered from 0 and upwards in thefrequency domain for subcarrier spacing configuration u. The center ofsubcarrier 0 of CRB 0 for subcarrier spacing configuration u coincideswith ‘point A’ which serves as a common reference point for resourceblock grids. In the 3GPP NR system, PRBs are defined within a bandwidthpart (BWP) and numbered from 0 to NsizeBWP,i-1, where i is the number ofthe bandwidth part. The relation between the physical resource blocknPRB in the bandwidth part i and the common resource block nCRB is asfollows: nPRB=nCRB+NsizeBWP,i, where NsizeBWP,i is the common resourceblock where bandwidth part starts relative to CRB 0. The BWP includes aplurality of consecutive RBs. A carrier may include a maximum of N(e.g., 5) BWPs. A UE may be configured with one or more BWPs on a givencomponent carrier. Only one BWP among BWPs configured to the UE canactive at a time. The active BWP defines the UE's operating bandwidthwithin the cell's operating bandwidth.

In the present disclosure, the term “cell” may refer to a geographicarea to which one or more nodes provide a communication system, or referto radio resources. A “cell” of a geographic area may be understood ascoverage within which a node can provide service using a carrier and a“cell” as radio resources (e.g. time-frequency resources) is associatedwith bandwidth (BW) which is a frequency range configured by thecarrier. The “cell” associated with the radio resources is defined by acombination of downlink resources and uplink resources, for example, acombination of a downlink (DL) component carrier (CC) and a uplink (UL)CC. The cell may be configured by downlink resources only, or may beconfigured by downlink resources and uplink resources. Since DLcoverage, which is a range within which the node is capable oftransmitting a valid signal, and UL coverage, which is a range withinwhich the node is capable of receiving the valid signal from the UE,depends upon a carrier carrying the signal, the coverage of the node maybe associated with coverage of the “cell” of radio resources used by thenode. Accordingly, the term “cell” may be used to represent servicecoverage of the node sometimes, radio resources at other times, or arange that signals using the radio resources can reach with validstrength at other times.

In carrier aggregation (CA), two or more CCs are aggregated. A UE maysimultaneously receive or transmit on one or multiple CCs depending onits capabilities. CA is supported for both contiguous and non-contiguousCCs. When CA is configured the UE only has one radio resource control(RRC) connection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell provides thenon-access stratum (NAS) mobility information, and at RRC connectionre-establishment/handover, one serving cell provides the security input.This cell is referred to as the Primary Cell (PCell). The PCell is acell, operating on the primary frequency, in which the UE eitherperforms the initial connection establishment procedure or initiates theconnection re-establishment procedure. Depending on UE capabilities,Secondary Cells (SCells) can be configured to form together with thePCell a set of serving cells. An SCell is a cell providing additionalradio resources on top of Special Cell. The configured set of servingcells for a UE therefore always consists of one PCell and one or moreSCells. For dual connectivity operation, the term Special Cell (SpCell)refers to the PCell of the master cell group (MCG) or the PSCell of thesecondary cell group (SCG). An SpCell supports PUCCH transmission andcontention-based random access, and is always activated. The MCG is agroup of serving cells associated with a master node, comprising of theSpCell (PCell) and optionally one or more SCells. The SCG is the subsetof serving cells associated with a secondary node, comprising of thePSCell and zero or more SCells, for a UE configured with dualconnectivity (DC). For a UE in RRC_CONNECTED not configured with CA/DCthere is only one serving cell comprising of the PCell. For a UE inRRC_CONNECTED configured with CA/DC the term “serving cells” is used todenote the set of cells comprising of the SpCell(s) and all SCells. InDC, two MAC entities are configured in a UE: one for the MCG and one forthe SCG.

FIG. 8 illustrates a data flow example in the 3GPP NR system.

In FIG. 8, “RB” denotes a radio bearer, and “H” denotes a header. Radiobearers are categorized into two groups: data radio bearers (DRB) foruser plane data and signalling radio bearers (SRB) for control planedata. The MAC PDU is transmitted/received using radio resources throughthe PHY layer to/from an external device. The MAC PDU arrives to the PHYlayer in the form of a transport block.

In the PHY layer, the uplink transport channels UL-SCH and RACH aremapped to their physical channels PUSCH and PRACH, respectively, and thedownlink transport channels DL-SCH, BCH and PCH are mapped to PDSCH,PBCH and PDSCH, respectively. In the PHY layer, uplink controlinformation (UCI) is mapped to PUCCH, and downlink control information(DCI) is mapped to PDCCH. A MAC PDU related to UL-SCH is transmitted bya UE via a PUSCH based on an UL grant, and a MAC PDU related to DL-SCHis transmitted by a BS via a PDSCH based on a DL assignment.

Data unit(s) (e.g. PDCP SDU, PDCP PDU, RLC SDU, RLC PDU, RLC SDU, MACSDU, MAC CE, MAC PDU) in the present disclosure is(are)transmitted/received on a physical channel (e.g. PDSCH, PUSCH) based onresource allocation (e.g. UL grant, DL assignment). In the presentdisclosure, uplink resource allocation is also referred to as uplinkgrant, and downlink resource allocation is also referred to as downlinkassignment. The resource allocation includes time domain resourceallocation and frequency domain resource allocation. In the presentdisclosure, an uplink grant is either received by the UE dynamically onPDCCH, in a Random Access Response, or configured to the UEsemi-persistently by RRC. In the present disclosure, downlink assignmentis either received by the UE dynamically on the PDCCH, or configured tothe UE semi-persistently by RRC signalling from the BS.

In various embodiments, timer value(s) as described in table 5 may beused.

TABLE 5 Timer Start Stop At expiry T300 Transmission of Reception ofRRCConnectionSetup, Perform RRC connection RRCConnectionRequest orRRCConnectionReject or establishment procedureRRCConnectionResumeRequest or RRCConnectionResume or RRCEarlyDataRequestRRCEarlyDataComplete or RRCConnectionRelease for UP-EDT, cellreselection and upon abortion of connection establishment by upperlayers T301 Transmission of Reception of Go to RRC_IDLERRCConnectionReestabilshmentRequest RRCConnectionReestablishment orRRCConnectionReestablishmentReject message as well as when the selectedcell becomes unsuitable T304 Reception of Criterion for successful Incase of cell change order RRCConnectionReconfiguration completion ofhandover from E-UTRA or intra E- message including the within E-UTRA,handover UTRA handover, initiate MobilityControl Info or to E-UTRA orcell change the RRC connection re- reception of order is met (thecriterion is establishment procedure; MobilityFromEUTRACommand specifiedin the target RAT In case of handover to E- message including in case ofinter-RAT) UTRA, perform the actions CellChangeOrder defined in thespecifications applicable for the source RAT. T311 Upon initiating theSelection of a suitable E- Enter RRC_IDLE RRC connection UTRA cell or acell using reestablishment procedure another RAT. T310 Upon detectingUpon receiving N311 If security is not activated physical layerconsecutive in-sync and the UE is not a NB-IoT problems for theindications from lower UE that supports RRC PCell i.e. upon layers forthe PCell, upon connection re- receiving N310 triggering the handoverestablishment for the consecutive out-of- procedure and upon ControlPlane CIoT EPS sync indications from initiating the connectionoptimisation: go to lower layers reestablishment procedure RRC_IDLEelse: initiate the connection reestablishment procedure T312 Upontriggering a Upon receiving N311 If security is not activated:measurement report consecutive in-sync go to RRC_IDLE else: for ameasurement indications from lower initiate the connection identity forwhich layers, upon triggering the reestablishment procedure T312 hasbeen handover procedure, upon configured, while initiating theconnection T310 is running reestablishment procedure, and upon theexpiry of T310

Further, in various embodiments, the constant N311 may be defined asmaximum number of consecutive “in-sync” or “early-in-sync” indicationsfor the PCell received from lower layers.

FIG. 9 shows an example of a dual connectivity (DC) architecture towhich technical features of the present disclosure can be applied.

Referring to FIG. 9, MN 911, SN 921, and a UE 930 communicating withboth the MN 911 and the SN 921 are illustrated. As illustrated in FIG.9, DC refers to a scheme in which a UE (e.g., UE 930) utilizes radioresources provided by at least two RAN nodes comprising a MN (e.g., MN911) and one or more SNs (e.g., SN 921). In other words, DC refers to ascheme in which a UE is connected to both the MN and the one or moreSNs, and communicates with both the MN and the one or more SNs. Sincethe MN and the SN may be in different sites, a backhaul between the MNand the SN may be construed as non-ideal backhaul (e.g., relativelylarge delay between nodes).

MN (e.g., MN 911) refers to a main RAN node providing services to a UEin DC situation. SN (e.g., SN 921) refers to an additional RAN nodeproviding services to the UE with the MN in the DC situation. If one RANnode provides services to a UE, the RAN node may be a MN. SN can existif MN exists.

For example, the MN may be associated with macro cell whose coverage isrelatively larger than that of a small cell. However, the MN does nothave to be associated with macro cell—that is, the MN may be associatedwith a small cell. Throughout the disclosure, a RAN node that isassociated with a macro cell may be referred to as ‘macro cell node’. MNmay comprise macro cell node.

For example, the SN may be associated with small cell (e.g., micro cell,pico cell, femto cell) whose coverage is relatively smaller than that ofa macro cell. However, the SN does not have to be associated with smallcell—that is, the SN may be associated with a macro cell. Throughout thedisclosure, a RAN node that is associated with a small cell may bereferred to as ‘small cell node’. SN may comprise small cell node.

The MN may be associated with a master cell group (MCG). MCG may referto a group of serving cells associated with the MN, and may comprise aprimary cell (PCell) and optionally one or more secondary cells(SCells). User plane data and/or control plane data may be transportedfrom a core network to the MN through a MCG bearer. MCG bearer refers toa bearer whose radio protocols are located in the MN to use MNresources. As shown in FIG. 9, the radio protocols of the MCG bearer maycomprise PDCP, RLC, MAC and/or PHY

The SN may be associated with a secondary cell group (SCG). SCG mayrefer to a group of serving cells associated with the SN, and maycomprise a primary secondary cell (PSCell) and optionally one or moreSCells. User plane data may be transported from a core network to the SNthrough a SCG bearer. SCG bearer refers to a bearer whose radioprotocols are located in the SN to use SN resources. As shown in FIG. 9,the radio protocols of the SCG bearer may comprise PDCP, RLC, MAC andPHY

User plane data and/or control plane data may be transported from a corenetwork to the MN and split up/duplicated in the MN, and at least partof the split/duplicated data may be forwarded to the SN through a splitbearer. Split bearer refers to a bearer whose radio protocols arelocated in both the MN and the SN to use both MN resources and SNresources. As shown in FIG. 9, the radio protocols of the split bearerlocated in the MN may comprise PDCP, RLC, MAC and PHY The radioprotocols of the split bearer located in the SN may comprise RLC, MACand PHY

According to various embodiments, PDCP anchor/PDCP anchor point/PDCPanchor node refers to a RAN node comprising a PDCP entity which splitsup and/or duplicates data and forwards at least part of thesplit/duplicated data over X2/Xn interface to another RAN node. In theexample of FIG. 9, PDCP anchor node may be MN.

According to various embodiments, the MN for the UE may be changed. Thismay be referred to as handover, or a MN handover.

According to various embodiments, a SN may newly start providing radioresources to the UE, establishing a connection with the UE, and/orcommunicating with the UE (i.e., SN for the UE may be newly added). Thismay be referred to as a SN addition.

According to various embodiments, a SN for the UE may be changed whilethe MN for the UE is maintained. This may be referred to as a SN change.

According to various embodiments, DC may comprise E-UTRAN NR-DC (EN-DC),and/or multi-radio access technology (RAT)-DC (MR-DC). EN-DC refers to aDC situation in which a UE utilizes radio resources provided by E-UTRANnode and NR RAN node. MR-DC refers to a DC situation in which a UEutilizes radio resources provided by RAN nodes with different RATs.

FIG. 10 shows an example of a handover procedure to which technicalfeatures of the present disclosure can be applied. FIG. 10 illustratessteps for the handover procedure exemplary, but the illustrated stepscan also be applied to a mobility procedure (e.g., SN addition procedureand/or SN change procedure).

Referring to FIG. 10, in step S1001, the source RAN node may transmitmeasurement control message to the UE. The source RAN node may configurethe UE measurement procedures according to the roaming and accessrestriction information and, for example, the available multiplefrequency band information through the measurement control message.Measurement control information provided by the source RAN node throughthe measurement control message may assist the function controlling theUE's connection mobility. For example, the measurement control messagemay comprise measurement configuration and/or report configuration.

In step S1003, the UE may transmit a measurement report message to thesource RAN node. The measurement report message may comprise a result ofmeasurement on neighbor cell(s) around the UE which can be detected bythe UE. The UE may generate the measurement report message according toa measurement configuration and/or measurement control information inthe measurement control message received in step S1001.

In step S1005, the source RAN node may make a handover (HO) decisionbased on the measurement report. For example, the source RAN node maymake a HO decision and determine a target RAN node for HO among neighborcells around the UE based on a result of measurement (e.g., cellquality, signal quality, signal strength, reference signal receivedpower (RSRP), reference signal received quality (RSRP), channel state,channel quality, signal to interference plus noise ratio (SINR)) on theneighbor cells.

In step S1007, the source RAN node may transmit a HO request message tothe target RAN node which is determined in step S1005. That is, thesource RAN node may perform handover preparation with the target RANnode. The HO request message may comprise necessary information toprepare the handover at the target RAN node.

In step S1009, the target RAN node may perform an admission controlbased on information included in the HO request message. The target RANnode may configure and reserve the required resources (e.g., C-RNTIand/or RACH preamble). The AS-configuration to be used in the target RANnode can either be specified independently (i.e. an “establishment”) oras a delta compared to the AS-configuration used in the source RAN node(i.e. a “reconfiguration”).

In step S1011, the target RAN node may transmit a HO request acknowledge(ACK) message to the source RAN node. The HO request ACK message maycomprise information on resources reserved and prepared for a handover.For example, the HO request ACK message may comprise a transparentcontainer to be sent to the UE as an RRC message to perform thehandover. The container may include a new C-RNTI, target gNB securityalgorithm identifiers for the selected security algorithms, a dedicatedRACH preamble, and/or possibly some other parameters i.e. accessparameters, SIBs. If RACH-less handover is configured, the container mayinclude timing adjustment indication and optionally a preallocateduplink grant. The HO request ACK message may also include RNL/TNLinformation for forwarding tunnels, if necessary. As soon as the sourceRAN node receives the HO request ACK message, or as soon as thetransmission of the handover command is initiated in the downlink, dataforwarding may be initiated.

In step S1013, the source RAN node may transmit a handover command whichmay be a RRC message, to the UE. The target RAN node may generate theRRC message to perform the handover, i.e. RRCConnectionReconfigurationmessage including the mobilityControlInformation, to be sent by thesource RAN node towards the UE. The source RAN node may perform thenecessary integrity protection and ciphering of the message. The UE mayreceive the RRCConnectionReconfiguration message with necessaryparameters (i.e. new C-RNTI, target eNB security algorithm identifiers,and optionally dedicated RACH preamble, target eNB SIBs, etc.) and iscommanded by the source eNB to perform the handover. If RACH-lesshandover is configured, the RRCConnectionReconfiguration may includetiming adjustment indication and optionally preallocated uplink grantfor accessing the target RAN node. If preallocated uplink grant is notincluded, the UE should monitor PDCCH of the target RAN node to receivean uplink grant. The UE may not need to delay the handover execution fordelivering the HARQ/ARQ responses to source RAN node. IfMake-Before-Break HO is configured, the connection to the source RANnode may be maintained after the reception ofRRCConnectionReconfiguration message with mobilityControlInformationbefore the UE executes initial uplink transmission to the target RANnode.

In step S1015, the UE may switch to a new cell i.e., the target RANnode. The UE may detach from the old cell i.e., the source RAN node andsynchronize to a new cell i.e., the target RAN node. For example, the UEmay perform a random access to the target RAN node. The UE may transmita random access preamble to the target RAN node, and receive a randomaccess response comprising an uplink grant from the target RAN node. IfRACH-less handover is configured, the step S1015 may be omitted, and theuplink grant may be provided in step S1013. The uplink grant may be usedfor the UE to transmit a handover complete message to the target RANnode.

In step S1017, the UE may transmit a handover complete message (i.e.,RRCConnectionReconfigurationComplete message) to the target RAN node.When the UE has successfully accessed the target RAN node or receiveduplink grant when RACH-less HO is configured, the UE may send theRRCConnectionReconfigurationComplete message comprising a C-RNTI toconfirm the handover, along with an uplink Buffer Status Report,whenever possible, to the target RAN node to indicate that the handoverprocedure is completed for the UE. The target RAN node may verify theC-RNTI sent in the RRCConnectionReconfigurationComplete message. Thetarget RAN node can now begin sending data to the UE.

FIG. 11 shows an example of a conditional handover procedure to whichtechnical features of the present disclosure can be applied. FIG. 11illustrates steps for the conditional handover procedure exemplary, butthe illustrated steps can also be applied to a conditional mobilityprocedure (e.g., conditional SN addition procedure and/or conditional SNchange procedure).

Referring to FIG. 11, in step S1101, the source RAN node may transmitmeasurement control message to the UE. The source RAN node may configurethe UE measurement procedures according to the roaming and accessrestriction information and, for example, the available multiplefrequency band information through the measurement control message.Measurement control information provided by the source RAN node throughthe measurement control message may assist the function controlling theUE's connection mobility. For example, the measurement control messagemay comprise measurement configuration and/or report configuration.

In step S1103, the UE may transmit a measurement report message to thesource RAN node. The measurement report message may comprise a result ofmeasurement on neighbor cell(s) around the UE which can be detected bythe UE. The UE may generate the measurement report message according toa measurement configuration and/or measurement control information inthe measurement control message received in step S1101.

In step S1105, the source RAN node may make a handover (HO) decisionbased on the measurement report. For example, the source RAN node maymake a HO decision and determine candidate target RAN nodes (e.g., cellquality, signal quality, signal strength, reference signal receivedpower (RSRP), reference signal received quality (RSRP), channel state,channel quality, signal to interference plus noise ratio (SINR)) on theneighbor cells.

In step S1107, the source RAN node may transmit HO request messages tothe target RAN node 1 and the target RAN node 2 which are determined instep S1105. That is, the source RAN node may perform handoverpreparation with the target RAN node 1 and the target RAN node 2. The HOrequest message may comprise necessary information to prepare thehandover at the target side (e.g., target RAN node 1 and target RAN node2).

In step S1109, each of the target RAN node 1 and the target RAN node 2may perform an admission control based on information included in the HOrequest message. The target RAN node may configure and reserve therequired resources (e.g., C-RNTI and/or RACH preamble). TheAS-configuration to be used in the target RAN node can either bespecified independently (i.e. an “establishment”) or as a delta comparedto the AS-configuration used in the source RAN node (i.e. a“reconfiguration”).

In step S1111, the target RAN node 1 and the target RAN node 2 maytransmit a HO request acknowledge (ACK) message to the source RAN node.The HO request ACK message may comprise information on resourcesreserved and prepared for a handover. For example, the HO request ACKmessage may comprise a transparent container to be sent to the UE as anRRC message to perform the handover. The container may include a newC-RNTI, target gNB security algorithm identifiers for the selectedsecurity algorithms, a dedicated RACH preamble, and/or possibly someother parameters i.e. access parameters, SIBs. If RACH-less handover isconfigured, the container may include timing adjustment indication andoptionally a preallocated uplink grant. The HO request ACK message mayalso include RNL/TNL information for forwarding tunnels, if necessary.As soon as the source RAN node receives the HO request ACK message, oras soon as the transmission of the handover command is initiated in thedownlink, data forwarding may be initiated.

In step S1113, the source RAN node may transmit a conditional HO (CHO)configuration to the UE. The CHO configuration may be also referred toas conditional reconfiguration. The CHO configuration may comprise a CHOconfiguration for each of the candidate target RAN nodes (e.g., targetRAN node 1, target RAN node 2). For example, the CHO configuration maycomprise a CHO configuration for the target RAN node 1, and a CHOconfiguration for the target RAN node 2. The CHO configuration for thetarget RAN node 1 may comprise a handover condition for the target RANnode 1, and a handover command of the target RAN node 1. The handovercommand of the target RAN node 1 may comprise RRC reconfigurationparameters for a handover to the target RAN node 1, includinginformation on resources reserved for the handover to the target RANnode 1. Similarly, the CHO configuration for the target RAN node 2 maycomprise a handover condition for the target RAN node 2, and a handovercommand of the target RAN node 2. The handover command of the target RANnode 2 may comprise RRC reconfiguration parameters for a handover to thetarget RAN node 2, including information on resources reserved for thehandover to the target RAN node 2.

In step S1115, the UE may perform an evaluation of the handovercondition for the candidate target RAN nodes (e.g., target RAN node 1,target RAN node 2) and select a target RAN node for handover among thecandidate target RAN nodes. For example, the UE may perform measurementson the candidate target RAN nodes, and determine whether a candidatetarget RAN node satisfies a handover condition for the candidate targetRAN node among the candidate target RAN nodes based on a result of themeasurements on the candidate target RAN nodes. If the UE identifiesthat the target RAN node 1 satisfies a handover condition for the targetRAN node 1, the UE may select the target RAN node 1 as a target RAN nodefor the handover.

In step S1117, the UE may perform a random access to the selected targetRAN node (e.g., target RAN node 1). For example, the UE may transmit arandom access preamble to the target RAN node 1, and receive a randomaccess response comprising an uplink grant from the target RAN node 1.If RACH-less handover is configured, the step S1117 may be omitted, andthe uplink grant may be provided in step S1113. The uplink grant may beused for the UE to transmit a HO complete message to the target RAN node1.

In step S1119, the UE may transmit a HO complete message to the targetRAN node 1. When the UE has successfully accessed the target RAN node 1(or, received uplink grant when RACH-less HO is configured), the UE maytransmit a HO complete message comprising a C-RNTI to confirm thehandover, along with uplink buffer status report, whenever possible, tothe target RAN node 1 to indicate that the handover procedure iscompleted for the UE. The target RAN node 1 may verify the C-RNTItransmitted in the HO complete message.

Throughout the disclosure, descriptions related to a handover may alsobe applied to a mobility including not only the handover but also an SNaddition and/or SN change.

Hereinafter, soft handover and/or dual active protocol stack (DAPS)handover is described.

Soft handover/handoff may refer to an ability to select between theinstantaneous received signals from different RAN nodes (i.e., sourceRAN node and target RAN node). In the soft handover/handoff, theconnection to the target RAN node may be established before theconnection to the source RAN node is broken. Hence, the softhandover/handoff may also be called “make-before-break (MBB)”handover/handoff. The main advantage of the soft handover/handoff may belowered probability of abnormal termination due to handover failure.

Also, DAPS handover refers to a handover based on DAPS in which both ofthe protocol stacks in a source RAN node and the protocol stacks in atarget RAN node may be active during the handover. That is, in the DAPSand/or the DAPS handover, radio bearers and configuration of a sourcecell and a target cell may be maintained until the source cell isreleased after a handover complete.

Detailed definition/features of the DAPS handover will be described inconjunction with FIGS. 12 to 14.

FIG. 12 shows an example of a state of source protocol and targetprotocol for a DAPS handover before initiating a handover and a randomaccess to which technical features of the present disclosure can beapplied.

Referring to FIG. 12, before initiating a handover, only source protocol(i.e., protocol stacks in a source RAN node) and source key (i.e., keyassociated with the source RAN node) may be used. The source protocolmay comprise at least one of PHY entity, MAC entity, RLC entity or PDCPentity.

Before initiating a random access, both the source protocol and a targetprotocol (i.e., protocol stacks in a target RAN node) may exist. Thetarget protocol may comprise at least one of PHY entity, MAC entity, RLCentity or PDCP entity. Also, both of the source key and a target key(i.e., key associated with the target RAN node) may exist. However, onlythe source protocol and the source key may be used before initiating therandom access when a UE has received a handover command.

FIG. 13 shows an example of a state of source protocol and targetprotocol for a DAPS handover during a random access and a transmissionof a handover complete message to which technical features of thepresent disclosure can be applied.

Referring to FIG. 13, during the random access, both of the sourceprotocol and the target protocol may exist. Also, both of the source keyand the target key may exist. The source protocol and the source key maybe used to receive/transmit data from/to the source RAN node. PHY entityand MAC entity of the target protocol may be used to perform the randomaccess procedure in the target RAN node. The RLC entity in the targetprotocol may be active for a contention-based random access procedure.

During the transmission of the handover complete message (i.e.,RRCConnectionReconfigurationComplete message), both of the sourceprotocol and the target protocol may exist. Also, both of the source keyand the target key may exist. The source protocol and the source key maybe used to receive/transmit data from/to the source RAN node. PHYentity, MAC entity and SRB PDCP entity of the target protocol may beused to perform the transmission of theRRCConnectionReconfigurationComplete message.

FIG. 14 shows an example of a state of source protocol and targetprotocol for a DAPS handover after RAR and a release of the source RANnode to which technical features of the present disclosure can beapplied.

Referring to FIG. 14, after a UE performing the DAPS handover hasreceived a random access response (RAR), both of the source protocol andthe target protocol may exist. Also, both of the source key and thetarget key may exist. The source protocol and the source key may be usedto receive/transmit data from/to the source RAN node. Further, targetprotocol and target key may be used to receive/transmit data from/to thetarget RAN node.

After a release of the source RAN node, the source protocol and thesource key may have been deleted. Only the target protocol and thetarget key may be used.

Throughout the disclosure, the terms ‘DAPS handover’, ‘softhandover/handoff’ and ‘MBB handover’ can be used inter-changeably.

According to various embodiments, a UE may receive anRRCConnectionReconfiguration message including a configuration parameter“mobilityControlInfo”. An example of the RRCConnectionReconfigurationmessage including mobilityControlInfo may be a handover command and/or aconditional handover command. If the UE receivedRRCConnectionReconfiguration message including mobilityControlInfo andthe UE is able to comply with the configuration included in theRRCConnectionReconfiguration message, the UE shall start synchornisingto a downlink of a target PCell. If a makeBeforeBreak (i.e., MBB) isconfigured, the UE may perform a handover procedure including resettingMAC entity after the UE has stopped the uplink transmission/downlinkreception with the source cell(s). It may be up to UE implementationwhen to stop the uplink transmission/downlink reception with the sourcecell(s) to initiate re-tuning for connection to the target cell, ifmakeBeforeBreak is configured.

According to various embodiments, upon receiving N310 consecutive“out-of-sync” indications for the PCell while neither T300, T301, T304nor T311 is running, the UE may start timer T310. Upon the T310 expiry,upon the T312 expiry, upon a random access problem indication from MCGMAC while neither T300, T301, T304 nor T311 is running, or uponindication from MCG RLC, which is allowed to be sent on PCell, that themaximum number of retransmissions has been reached for an SRB or DRB,the UE may consider a radio link failure (RLF) to be detected for theMCG.

According to various embodiments, the UE may initiate the RRCreestablishment procedure upon detecting the RLF of the MCG, and/or uponre-configuration with sync failure of the MCG.

Hereinafter, radio link monitoring (RLM) handling during MBB handover isdescribed.

According to various embodiments, the UE may continue RLM on source cellconnection even after receiving the MBB handover command, until a randomaccess to the target cell is successful or the UE successfully receivesa PDCCH transmission in case of RACH-less handover.

According to various embodiments, the UE may perform RLM only on targetcell connection once the MBB handover execution to the target cell issuccessful. That is, the UE may perform RLM only on target cellconnection once the random access to the target cell is successful orthe UE successfully receives the PDCCH transmission in case of RACH-lesshandover.

According to various embodiments, when the RLF is detected on the targetcell after successful HO completion and if the source cell connection isnot yet released by the UE, then the UE may resume RLM on the sourcecell on fallback to the source cell connection.

Hereinafter, RLF handling during MBB handover is described.

According to various embodiments, on detecting an MBB handover failure(e.g., T304 expiry) or on detecting RLF on target cell connection (whilethe source cell connection is active) during the MBB handover, the UEmay declare RLF on target cell connection but may not trigger RRCreestablishment and may operate using the source cell connection.

According to various embodiments, the UE may send RLF information to thesource cell including an appropriate failure cause and any availablemeasurement results on the target cell.

According to various embodiments, the UE may trigger RRCre-establishment during an MBB handover only when both the source cellconnection and the target cell connection fail, due to RLF or MBBhandover failure.

As one of enhancements of MBB handover, DAPS solution is underdiscussion to achieve 0 ms interruption time during a mobility. For theDAPS, radio bearers of source cell and target cell may be maintaineduntil target cell may transmit RRC reconfiguration message to releasesource cell configuration. In order to achieve 0 ms interruption time,the source cell may assign which DL data is rather transferred by thetarget cell while other DL/UL data are being transferred via the sourcecell during a handover, and the UE would receive/transmit DL/UL datafrom/to the target cell only and the target cell may indicate to thesource cell that path can be switched from the source cell to the targetcell after a handover complete.

However, since multiple connections for the source cell and the targetcell should be alive in the DAPS solution, RLM handling issue may beraised. The problem is that how to start and/or how to end performingRLM on the source cell and/or the target cell. If the UE performs RLM onthe side of source cell during a DAPS handover, there should beadditional handling when RLF is detected on the source cell. Forexample, if the RLF is occurred at source cell during a handover but thesource cell keeps trying to send residual data which is assigned to thesource cell, data transfer may be delayed if the source cell still triesto handle residual data after a handover complete. In addition, if thetarget cell is in charge of signalling to release the source cell,unnecessary signalling could be transferred even though the sourcecell's configuration had already released.

Therefore, there should be an additional behaviour to handle source cellRLM during performing the dual active protocol stack HO as MBBenhancement.

FIG. 15 shows an example of a method for an MBB mobility according to anembodiment of the present disclosure. Steps illustrated in FIG. 15 maybe performed by a UE and/or a wireless device.

Referring to FIG. 15, in step S1501, the wireless device may perform aDAPS mobility procedure for a mobility from a source cell to a targetcell while maintaining a radio link for the source cell. The DAPSmobility procedure may comprise a mobility procedure in which both ofprotocol stacks in the source cell and protocol stacks in the targetcell are active during the mobility procedure, or radio bearers and aconfiguration of the source cell and the target cell is maintained untilthe source cell is released.

In step S1503, the wireless device may perform an RLM comprising amonitoring of a number of consecutive out-of-sync indications receivedon a radio link for the source cell during the DAPS mobility procedureThe wireless device may detect the RLF for the source cell based on thatthe number of received consecutive out-of-sync indications reaches athreshold number (e.g., N310). The threshold number comprises at leastone of a predetermined threshold value, or a threshold value receivedfrom a network (e.g., source cell and/or target cell).

In step S1505, the wireless device may detect an RLF on the radio linkfor the source cell based on the RLM. For example, the wireless devicemay declare the RLF upon an expiry of a timer (e.g., T304). The timermay start upon receiving the consecutive out of sync indications of thethreshold number on the radio link for the source cell. The wirelessdevice may, upon an expiry of the timer for the source cell, detect theRLF on the radio link for the source cell. The wireless device may alsodetect the RLF on the radio link for the source cell upon the T312expiry, upon a random access problem indication from MCG MAC whileneither T300, T301, T304 nor T311 is running, or upon indication fromMCG RLC that the maximum number of retransmissions has been reached foran SRB or DRB.

In step S1507, the wireless device may stop a transmission on the radiolink for the source cell during the DAPS mobility procedure. Forexample, the wireless device may communicate with the source cell basedon a source cell configuration during the DAPS mobility procedure. Thewireless device may release the source cell configuration after/upondetecting the RLF on the radio link for the source cell. The source cellconfiguration may be a configuration used for the wireless device tocommunicate with the source cell during the DAPS handover procedure.

According to various embodiments, the wireless device may transmit, tothe target cell, an RLF indication indicating the RLF on the radio linkfor the source cell. The RLF indication may inform that the source cellis released by the RLF during the DAPS handover procedure.

According to various embodiments, the wireless device may transmit, tothe target cell, a mobility complete message comprising the RLFindication.

According to various embodiments, the RLF indication may comprise atleast one of measurement results on the source cell, or a cause of theRLF. The cause of the RLF may comprise at least one of a MAC randomaccess problem, or T310 expiry.

According to various embodiments, the wireless device may release thesource cell configuration without receiving, from the target cell, anindication to release the source cell configuration.

According to various embodiments, the wireless device may receive, fromthe source cell, an indication to perform operations related to a DAPShandover. The wireless device may initiate the DAPS handover procedureupon a reception of the indication.

According to various embodiments, the wireless device may perform an RLMon a radio link for the target cell. For example, the wireless devicemay perform an RLM on a radio link for the target cell during the DAPSmobility procedure.

According to various embodiments, the wireless device may perform theRLM on the radio link for the source cell until transmitting a mobilitycomplete message to the target cell. The wireless device may perform theRLM on the radio link for the target cell after transmitting thehandover complete message to the target cell.

According to various embodiments, the wireless device may perform amobility from a source cell to a target cell while maintaining aconfiguration of the source cell including a radio bearer. The wirelessdevice may monitor a radio link of the source cell while performing themobility. The wireless device may stop monitoring the radio link andrelease the configuration of the source cell when detecting a radio linkfailure on the source cell. The wireless device may indicate to thetarget cell that the source cell which was supposed to be maintainedduring the mobility has already released by the radio link failure whentransmitting a mobility complete message (e.g.,RRCReconfigurationComplete message) to the target cell.

FIG. 16A and FIG. 16B show an example of a signal flow for RLM handlingduring a MBB handover according to an embodiment of the presentdisclosure.

First, FIG. 16A is described.

In step S1601, the UE may transmit a measurement report message to thesource RAN node. The measurement report message may comprise a result ofmeasurement on neighbor cell(s) around the UE which can be detected bythe UE. The UE may generate the measurement report message according toa measurement configuration and/or measurement control information inthe measurement control message received from the source RAN node. Thesource RAN node may make a handover (HO) decision based on themeasurement report. For example, the source RAN node may make a HOdecision and determine a target RAN node for HO among neighbor cellsaround the UE based on a result of measurement (e.g., cell quality,signal quality, signal strength, reference signal received power (RSRP),reference signal received quality (RSRP), channel state, channelquality, signal to interference plus noise ratio (SINR)) on the neighborcells.

In step S1603, the source RAN node may transmit a HO request message tothe target RAN node. That is, the source RAN node may perform handoverpreparation with the target RAN node. The HO request message maycomprise necessary information to prepare the handover at the target RANnode. Further, according to various embodiments, the HO request messagemay further comprise DAPS indication informing that a DAPS handover willbe performed.

In step S1605, the target RAN node may transmit a HO request acknowledge(ACK) message to the source RAN node. The HO request ACK message maycomprise information on resources reserved and prepared for a handover.

In step S1607, the UE may receive, from a source cell associated withthe source RAN node, a handover command which is a kind of aRRCReconfiguration message and enhanced MBB indication for handover. Theenhanced MBB indication may be used to perform operations related toDAPS. For DAPS, RLM on the source cell may be required until the UEsends a HO complete message to a target cell associated with the targetRAN node and RLM on the target cell may be required from the time the UEsent the HO complete message to the target cell. Based on the DAPSconfiguration received from the source RAN node, the UE may maintainsource cell's configuration during the DAPS handover. Further, thesource RAN node may assign data to the UE during the DAPS handover.

In step S1609, the UE may try to perform a random access to the targetcell while maintaining a source cell connection. For example, the UE maytransmit a random access preamble to the target cell. The target cellmay response to the random access trial. The target cell may transmit arandom access response for the random access preamble to the UE. Thesource RAN node may keep scheduling of UL/DL data so that the UE maytransmit UL data to the source RAN node and receive DL data from thesource RAN node. The UE may keep monitoring a radio link on the sourcecell. For example, the UE may perform RLM on the source cell whileperforming a random access to the target cell.

In step S1611, the UE may declare RLF on the source cell. For example,the UE may declare RLF on the source cell after receiving N310consecutive out-of-sync indications during the handover. Then, the UEmay stop UL/DL data transmission with the source cell. The UE mayfurther release whole source cell configuration. The source RAN node maykeep trying to transmit residual data.

In step S1613, the UE may indicate an RLF indication of the source cellto the target cell when transmitting HO complete message (i.e.,RRCReconfigurationComplete message) to the target cell. The RLFindication of the source cell may be included in the HO complete message(i.e., RRCReconfigurationComplete message). The RLF indication of thesource cell may indicate that the source cell which was supposed to bemaintained during the handover procedure has already released by theRLF. The RLF indication may include at least one of i) measurementresults on the source cell (e.g., RSRP/RSRQ), or ii) RLF cause (e.g.,MAC random access problem, T310 expiry).

Next, FIG. 16B which follows FIG. 16A is described.

In step S1615, upon receiving the handover complete message includingthe RLF indication of the source cell, the target RAN node may transmita handover success indication including the RLF indication to the sourcecell.

In step S1617, upon receiving the handover success indication includingthe RLF indication from the target cell, the source cell may stop datatransmission to the UE. Even though there are residual data which wouldnot be scheduled to the target cell, the source cell may forward theresidual data to the target cell. If the target cell is supposed to sendRRC signalling to release the source cell configuration in a normal MBBhandover procedure (i.e., the normal MBB handover procedure in which thetarget cell transmits a handover success indication without the RLFindication to the source cell, the target cell may not wait forreceiving acknowledge (ACK) message for the handover success indicationfrom the source cell and may not send a RRC signalling to the UE torelease the source cell configuration.

Hereinafter, steps for performing RLM on the source cell during the DAPSmobility procedure will be described.

With regard to reconfiguration with sync, the UE shall perform thefollowing actions to execute a reconfiguration with sync:

1> if the AS security is not activated, perform the actions upon goingto RRC_IDLE with the release cause ‘other’ upon which the procedureends;

1> If dapsConfig is not configured for any DRB:

2> stop timer T310 for the corresponding SpCell, if running;

1> stop timer T312 for the corresponding SpCell, if running;

1> start timer T304 for the corresponding SpCell with the timer valueset to t304, as included in the reconfigurationWithSync;

With regard to detection of physical layer problems in RRC_CONNECTED,the UE shall:

1> if dapsConfig is configured for any DRB, upon receiving N310consecutive “out-of-sync” indications for the source from lower layerswhile T304 is running:

2> start timer T310 for the source.

With regard to detection of radio link failure, the UE shall:

1> if dapsConfig is configured for any DRB:

2> upon T310 expiry in source; or

2> upon random access problem indication from source MCG MAC; or

2> upon indication from source MCG RLC that the maximum number ofretransmissions has been reached:

3> consider radio link failure to be detected for the source MCG i.e.source RLF;

4> suspend all DRBs in the source;

4> release the source connection.

FIG. 17 shows a UE to implement an embodiment of the present disclosure.The present disclosure described above for UE side may be applied tothis embodiment.

A UE includes a processor 1710, a power management module 1711, abattery 1712, a display 1713, a keypad 1714, a subscriber identificationmodule (SIM) card 1715, a memory 1720, a transceiver 1730, one or moreantennas 1731, a speaker 1740, and a microphone 1741.

The processor 1710 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 1710. Theprocessor 1710 may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Theprocessor 1710 may be an application processor (AP). The processor 1710may include at least one of a digital signal processor (DSP), a centralprocessing unit (CPU), a graphics processing unit (GPU), a modem(modulator and demodulator). An example of the processor 1710 may befound in SNAPDRAGON™ series of processors made by Qualcomm®, EXYNOS™series of processors made by Samsung®, A series of processors made byApple®, HELIO™ series of processors made by MediaTek®, ATOM™ series ofprocessors made by Intel® or a corresponding next generation processor.

The processor 1710 may be configured to, or configured to control thetransceiver 1730 to implement steps performed by the UE and/or thewireless device throughout the disclosure.

The power management module 1711 manages power for the processor 1710and/or the transceiver 1730. The battery 1712 supplies power to thepower management module 1711. The display 1713 outputs results processedby the processor 1710. The keypad 1714 receives inputs to be used by theprocessor 1710. The keypad 1714 may be shown on the display 1713. TheSIM card 1715 is an integrated circuit that is intended to securelystore the international mobile subscriber identity (IMSI) number and itsrelated key, which are used to identify and authenticate subscribers onmobile telephony devices (such as mobile phones and computers). It isalso possible to store contact information on many SIM cards.

The memory 1720 is operatively coupled with the processor 1710 andstores a variety of information to operate the processor 1710. Thememory 1720 may include read-only memory (ROM), random access memory(RAM), flash memory, memory card, storage medium and/or other storagedevice. When the embodiments are implemented in software, the techniquesdescribed herein can be implemented with modules (e.g., procedures,functions, and so on) that perform the functions described herein. Themodules can be stored in the memory 1720 and executed by the processor1710. The memory 1720 can be implemented within the processor 1710 orexternal to the processor 1710 in which case those can becommunicatively coupled to the processor 1710 via various means as isknown in the art.

The transceiver 1730 is operatively coupled with the processor 1710, andtransmits and/or receives a radio signal. The transceiver 1730 includesa transmitter and a receiver. The transceiver 1730 may include basebandcircuitry to process radio frequency signals. The transceiver 1730controls the one or more antennas 1731 to transmit and/or receive aradio signal.

The speaker 1740 outputs sound-related results processed by theprocessor 1710. The microphone 1741 receives sound-related inputs to beused by the processor 1710.

FIG. 18 shows another example of a wireless communication system towhich the technical features of the present disclosure can be applied.

Referring to FIG. 18, the wireless communication system may include afirst device 1810 (i.e., first device 210) and a second device 1820(i.e., second device 220).

The first device 1810 may include at least one transceiver, such as atransceiver 1811, and at least one processing chip, such as a processingchip 1812. The processing chip 1812 may include at least one processor,such a processor 1813, and at least one memory, such as a memory 1814.The memory may be operably connectable to the processor 1813. The memory1814 may store various types of information and/or instructions. Thememory 1814 may store a software code 1815 which implements instructionsthat, when executed by the processor 1813, perform operations of thefirst device 910 described throughout the disclosure. For example, thesoftware code 1815 may implement instructions that, when executed by theprocessor 1813, perform the functions, procedures, and/or methods of thefirst device 1810 described throughout the disclosure. For example, thesoftware code 1815 may control the processor 1813 to perform one or moreprotocols. For example, the software code 1815 may control the processor1813 to perform one or more layers of the radio interface protocol.

The second device 1820 may include at least one transceiver, such as atransceiver 1821, and at least one processing chip, such as a processingchip 1822. The processing chip 1822 may include at least one processor,such a processor 1823, and at least one memory, such as a memory 1824.The memory may be operably connectable to the processor 1823. The memory1824 may store various types of information and/or instructions. Thememory 1824 may store a software code 1825 which implements instructionsthat, when executed by the processor 1823, perform operations of thesecond device 1820 described throughout the disclosure. For example, thesoftware code 1825 may implement instructions that, when executed by theprocessor 1823, perform the functions, procedures, and/or methods of thesecond device 1820 described throughout the disclosure. For example, thesoftware code 1825 may control the processor 1823 to perform one or moreprotocols. For example, the software code 1825 may control the processor1823 to perform one or more layers of the radio interface protocol.

The present disclosure may be applied to various future technologies,such as AI, robots, autonomous-driving/self-driving vehicles, and/orextended reality (XR).

<AI>

AI refers to artificial intelligence and/or the field of studyingmethodology for making it. Machine learning is a field of studyingmethodologies that define and solve various problems dealt with in AI.Machine learning may be defined as an algorithm that enhances theperformance of a task through a steady experience with any task.

An artificial neural network (ANN) is a model used in machine learning.It can mean a whole model of problem-solving ability, consisting ofartificial neurons (nodes) that form a network of synapses. An ANN canbe defined by a connection pattern between neurons in different layers,a learning process for updating model parameters, and/or an activationfunction for generating an output value. An ANN may include an inputlayer, an output layer, and optionally one or more hidden layers. Eachlayer may contain one or more neurons, and an ANN may include a synapsethat links neurons to neurons. In an ANN, each neuron can output asummation of the activation function for input signals, weights, anddeflections input through the synapse. Model parameters are parametersdetermined through learning, including deflection of neurons and/orweights of synaptic connections. The hyper-parameter means a parameterto be set in the machine learning algorithm before learning, andincludes a learning rate, a repetition number, a mini batch size, aninitialization function, etc. The objective of the ANN learning can beseen as determining the model parameters that minimize the lossfunction. The loss function can be used as an index to determine optimalmodel parameters in learning process of ANN.

Machine learning can be divided into supervised learning, unsupervisedlearning, and reinforcement learning, depending on the learning method.Supervised learning is a method of learning ANN with labels given tolearning data. Labels are the answers (or result values) that ANN mustinfer when learning data is input to ANN. Unsupervised learning can meana method of learning ANN without labels given to learning data.Reinforcement learning can mean a learning method in which an agentdefined in an environment learns to select a behavior and/or sequence ofactions that maximizes cumulative compensation in each state.

Machine learning, which is implemented as a deep neural network (DNN)that includes multiple hidden layers among ANN, is also called deeplearning. Deep learning is part of machine learning. In the following,machine learning is used to mean deep learning.

FIG. 19 shows an example of an AI device to which the technical featuresof the present disclosure can be applied.

The AI device 1900 may be implemented as a stationary device or a mobiledevice, such as a TV, a projector, a mobile phone, a smartphone, adesktop computer, a notebook, a digital broadcasting terminal, a PDA, aPMP, a navigation device, a tablet PC, a wearable device, a set-top box(STB), a digital multimedia broadcasting (DMB) receiver, a radio, awashing machine, a refrigerator, a digital signage, a robot, a vehicle,etc.

Referring to FIG. 19, the AI device 1900 may include a communicationpart 1910, an input part 1920, a learning processor 1930, a sensing part1940, an output part 1950, a memory 1960, and a processor 1970.

The communication part 1910 can transmit and/or receive data to and/orfrom external devices such as the AI devices and the AI server usingwire and/or wireless communication technology. For example, thecommunication part 1910 can transmit and/or receive sensor information,a user input, a learning model, and a control signal with externaldevices. The communication technology used by the communication part1910 may include a global system for mobile communication (GSM), a codedivision multiple access (CDMA), an LTE/LTE-A, a 5G, a WLAN, a Wi-Fi,Bluetooth™, radio frequency identification (RFID), infrared dataassociation (IrDA), ZigBee, and/or near field communication (NFC).

The input part 1920 can acquire various kinds of data. The input part1920 may include a camera for inputting a video signal, a microphone forreceiving an audio signal, and a user input part for receivinginformation from a user. A camera and/or a microphone may be treated asa sensor, and a signal obtained from a camera and/or a microphone may bereferred to as sensing data and/or sensor information. The input part1920 can acquire input data to be used when acquiring an output usinglearning data and a learning model for model learning. The input part1920 may obtain raw input data, in which case the processor 1970 or thelearning processor 1930 may extract input features by preprocessing theinput data.

The learning processor 1930 may learn a model composed of an ANN usinglearning data. The learned ANN can be referred to as a learning model.The learning model can be used to infer result values for new input datarather than learning data, and the inferred values can be used as abasis for determining which actions to perform. The learning processor1930 may perform AI processing together with the learning processor ofthe AI server. The learning processor 1930 may include a memoryintegrated and/or implemented in the AI device 1900. Alternatively, thelearning processor 1930 may be implemented using the memory 1960, anexternal memory directly coupled to the AI device 1900, and/or a memorymaintained in an external device.

The sensing part 1940 may acquire at least one of internal informationof the AI device 1900, environment information of the AI device 1900,and/or the user information using various sensors. The sensors includedin the sensing part 1940 may include a proximity sensor, an illuminancesensor, an acceleration sensor, a magnetic sensor, a gyro sensor, aninertial sensor, an RGB sensor, an IR sensor, a fingerprint recognitionsensor, an ultrasonic sensor, an optical sensor, a microphone, a lightdetection and ranging (LIDAR), and/or a radar.

The output part 1950 may generate an output related to visual, auditory,tactile, etc. The output part 1950 may include a display unit foroutputting visual information, a speaker for outputting auditoryinformation, and/or a haptic module for outputting tactile information.

The memory 1960 may store data that supports various functions of the AIdevice 1900. For example, the memory 1960 may store input data acquiredby the input part 1920, learning data, a learning model, a learninghistory, etc.

The processor 1970 may determine at least one executable operation ofthe AI device 1900 based on information determined and/or generatedusing a data analysis algorithm and/or a machine learning algorithm. Theprocessor 1970 may then control the components of the AI device 1900 toperform the determined operation. The processor 1970 may request,retrieve, receive, and/or utilize data in the learning processor 1930and/or the memory 1960, and may control the components of the AI device1900 to execute the predicted operation and/or the operation determinedto be desirable among the at least one executable operation. Theprocessor 1970 may generate a control signal for controlling theexternal device, and may transmit the generated control signal to theexternal device, when the external device needs to be linked to performthe determined operation. The processor 1970 may obtain the intentioninformation for the user input and determine the user's requirementsbased on the obtained intention information. The processor 1970 may useat least one of a speech-to-text (STT) engine for converting speechinput into a text string and/or a natural language processing (NLP)engine for acquiring intention information of a natural language, toobtain the intention information corresponding to the user input. Atleast one of the STT engine and/or the NLP engine may be configured asan ANN, at least a part of which is learned according to a machinelearning algorithm. At least one of the STT engine and/or the NLP enginemay be learned by the learning processor 1930 and/or learned by thelearning processor of the AI server, and/or learned by their distributedprocessing. The processor 1970 may collect history information includingthe operation contents of the AI device 1900 and/or the user's feedbackon the operation, etc. The processor 1970 may store the collectedhistory information in the memory 1960 and/or the learning processor1930, and/or transmit to an external device such as the AI server. Thecollected history information can be used to update the learning model.The processor 1970 may control at least some of the components of AIdevice 1900 to drive an application program stored in memory 1960.Furthermore, the processor 1970 may operate two or more of thecomponents included in the AI device 1900 in combination with each otherfor driving the application program.

FIG. 20 shows an example of an AI system to which the technical featuresof the present disclosure can be applied.

Referring to FIG. 20, in the AI system, at least one of an AI server2020, a robot 2010 a, an autonomous vehicle 2010 b, an XR device 2010 c,a smartphone 2010 d and/or a home appliance 2010 e is connected to acloud network 2000. The robot 2010 a, the autonomous vehicle 2010 b, theXR device 2010 c, the smartphone 2010 d, and/or the home appliance 2010e to which the AI technology is applied may be referred to as AI devices2010 a to 2010 e.

The cloud network 2000 may refer to a network that forms part of a cloudcomputing infrastructure and/or resides in a cloud computinginfrastructure. The cloud network 2000 may be configured using a 3Gnetwork, a 4G or LTE network, and/or a 5G network. That is, each of thedevices 2010 a to 2010 e and 2020 consisting the AI system may beconnected to each other through the cloud network 2000. In particular,each of the devices 2010 a to 2010 e and 2020 may communicate with eachother through a base station, but may directly communicate with eachother without using a base station.

The AI server 2020 may include a server for performing AI processing anda server for performing operations on big data. The AI server 2020 isconnected to at least one or more of AI devices constituting the AIsystem, i.e. the robot 2010 a, the autonomous vehicle 2010 b, the XRdevice 2010 c, the smartphone 2010 d and/or the home appliance 2010 ethrough the cloud network 2000, and may assist at least some AIprocessing of the connected AI devices 2010 a to 2010 e. The AI server2020 can learn the ANN according to the machine learning algorithm onbehalf of the AI devices 2010 a to 2010 e, and can directly store thelearning models and/or transmit them to the AI devices 2010 a to 2010 e.The AI server 2020 may receive the input data from the AI devices 2010 ato 2010 e, infer the result value with respect to the received inputdata using the learning model, generate a response and/or a controlcommand based on the inferred result value, and transmit the generateddata to the AI devices 2010 a to 2010 e. Alternatively, the AI devices2010 a to 2010 e may directly infer a result value for the input datausing a learning model, and generate a response and/or a control commandbased on the inferred result value.

Various embodiments of the AI devices 2010 a to 2010 e to which thetechnical features of the present disclosure can be applied will bedescribed. The AI devices 2010 a to 2010 e shown in FIG. 20 can be seenas specific embodiments of the AI device 1900 shown in FIG. 19.

The present disclosure can have various advantageous effects.

For example, a wireless device may perform an RLM on a source cellduring a DAPS mobility procedure and stop a transmission on the sourcecell after detecting an RLF on the source cell based on the RLM.Therefore, unnecessary transmission to the source cell and unnecessarymonitoring on a downlink from the source cell can be avoided, and thuspower consumption in the wireless device can be reduced.

For example, when a target cell receives a mobility complete messageincluding RLF indication of a source cell, the target cell can requestthe source cell to stop handling residual data on the source cell.Therefore, additional data interruption which can be occurred by thesource cell still trying to handle the residual data can be reduced.Additionally, after a mobility complete, the target cell may not need toconfigure RRC reconfiguration to release the source cell.

Advantageous effects which can be obtained through specific embodimentsof the present disclosure are not limited to the advantageous effectslisted above. For example, there may be a variety of technical effectsthat a person having ordinary skill in the related art can understandand/or derive from the present disclosure. Accordingly, the specificeffects of the present disclosure are not limited to those explicitlydescribed herein, but may include various effects that may be understoodor derived from the technical features of the present disclosure.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope of the present disclosure.

Claims in the present description can be combined in a various way. Forinstance, technical features in method claims of the present descriptioncan be combined to be implemented or performed in an apparatus, andtechnical features in apparatus claims can be combined to be implementedor performed in a method. Further, technical features in method claim(s)and apparatus claim(s) can be combined to be implemented or performed inan apparatus. Further, technical features in method claim(s) andapparatus claim(s) can be combined to be implemented or performed in amethod. Other implementations are within the scope of the followingclaims.

What is claimed is:
 1. A method performed by a wireless device in a wireless communication system, the method comprising: initiating, by the wireless device, a dual active protocol stack (DAPS) mobility procedure for a mobility from a source cell to a target cell, wherein a radio link for the source cell and a radio link for the target cell are maintained during the DAPS mobility procedure; monitoring, by the wireless device while performing a random access to the target cell in the DAPS mobility procedure, a number of consecutive out-of-sync indications received on a radio link for the source cell for a radio link monitoring (RLM) on the radio link for the source cell; and after detecting a radio link failure (RLF) for the source cell based on the RLM, stopping, by the wireless device, a transmission on the radio link for the source cell during the DAPS mobility procedure.
 2. The method of claim 1, wherein the detecting of the RLF comprises: detecting the RLF for the source cell based on that the number of received consecutive out-of-sync indications reaches a threshold number, wherein the threshold number comprises at least one of a predetermined threshold value, or a threshold value received from a network.
 3. The method of claim 2, wherein the detecting of the RLF comprises: declaring the RLF upon an expiry of a timer, wherein the timer starts upon receiving the consecutive out of sync indications of the threshold number on the radio link for the source cell.
 4. The method of claim 1, further comprising: transmitting, to the target cell, an RLF indication indicating the RLF on the radio link for the source cell, wherein the RLF indication comprises at least one of measurement results, or a cause of the RLF.
 5. The method of claim 4, wherein the transmitting of the RLF indication comprises transmitting, to the target cell, a mobility complete message comprising the RLF indication.
 6. The method of claim 1, further comprising: communicating with the source cell based on a source cell configuration during the DAPS mobility procedure; and releasing the source cell configuration after detecting the RLF on the radio link for the source cell.
 7. The method of claim 6, wherein the releasing of the source cell configuration comprises: releasing the source cell configuration without receiving, from the target cell, an indication to release the source cell configuration.
 8. The method of claim 1, further comprising: receiving, from the source cell, an indication to perform operations related to a DAPS handover; and initiating the DAPS handover procedure upon a reception of the indication.
 9. The method of claim 1, further comprising: performing an RLM on a radio link for the target cell.
 10. The method of claim 9, wherein the performing of the RLM on the radio link for the source cell comprises performing the RLM on the radio link for the source cell until transmitting a mobility complete message to the target cell, and wherein the performing of the RLM on the radio link for the target cell comprises performing the RLM on the radio link for the target cell after transmitting the handover complete message to the target cell.
 11. The method of claim 1, wherein the DAPS mobility procedure is a mobility procedure in which: both of protocol stacks in the source cell and protocol stacks in the target cell are active during the mobility procedure; or radio bearers and a configuration of the source cell and the target cell are maintained until the source cell is released.
 12. The method of claim 1, wherein the wireless device is in communication with at least one of a user equipment, a network, and/or autonomous vehicles other than the wireless device.
 13. A wireless device in a wireless communication system comprising: a transceiver; a memory; and at least one processor operatively coupled to the transceiver and the memory, and configured to: initiate a dual active protocol stack (DAPS) mobility procedure for a mobility from a source cell to a target cell, wherein a radio link for the source cell and a radio link for the target cell are maintained during the DAPS mobility procedure; monitor, while performing a random access to the target cell in the DAPS mobility procedure, a number of consecutive out-of-sync indications received on a radio link for the source cell for a radio link monitoring (RLM) on the radio link for the source cell; and after detecting a radio link failure (RLF) for the source cell based on the RLM, stop a transmission on the radio link for the source cell during the DAPS mobility procedure.
 14. The wireless device of claim 13, wherein the at least one processor is further configured to control the transceiver to transmit, to the target cell, an RLF indication indicating the RLF on the radio link for the source cell, wherein the RLF indication comprises at least one of measurement results, or a cause of the RLF.
 15. A processor for a wireless device in a wireless communication system, wherein the processor is configured to control the wireless device to perform operations comprising: initiating a dual active protocol stack (DAPS) mobility procedure for a mobility from a source cell to a target cell, wherein a radio link for the source cell and a radio link for the target cell are maintained during the DAPS mobility procedure; monitoring, while performing a random access to the target cell in the DAPS mobility procedure, a number of consecutive out-of-sync indications received on a radio link for the source cell for a radio link monitoring (RLM) on the radio link for the source cell; and after detecting a radio link failure (RLF) for the source cell based on the RLM, stopping a transmission on the radio link for the source cell during the DAPS mobility procedure.
 16. The processor of claim 15, wherein the operations further comprise: transmitting, to the target cell, an RLF indication indicating the RLF on the radio link for the source cell, wherein the RLF indication comprises at least one of measurement results, or a cause of the RLF. 